Wellingborough CLs

Not one that we've used, but Northfield Farm, Cransley, No 1180 in SD, may fit the bill. It has been recommended in the past on CT. Another could be Rockingham Vally CL, Corby, No.856 in SD, has been recommended in the past by Rocky.

Hope that you get fixed up with a site that suits your requirements. Please let me know how you get on, as we are always on the lookout for decent CLs in areas that we've seldom, if ever visited.

This one has not got the hardstanding but I have found it a good firm site, with EHU.

Glebe Farm - 32 Overstone Road, Sywell, Northampton, NN6 0AW

https://www.caravanclub.co.uk/certificated-locations/england/northamptonshire/northampton/glebe-farm-1/

View it on Google maps in satellite, it has a firm gravel entry track.

Edit: looks if they may have hardstandings now?